This invention concerns wastewater treatment, and in particular a modification of the manner in which settled sludge is withdrawn from the bottom of a clarifier tank.
In a conventional wastewater treatment plant, wastewater is fed into one or more clarifier tanks, where solids are settled to the bottom of the tank, gathered toward the center of the sloping tank bottom by the rake arms of a rotating rake, then discharged out of the tank through a bottom exit pipe installed beneath the concrete floor surface. This type of installation can present problems, such as corrosion, clogging or failure of a pipe beneath the surface, lack of such an exit pipe in a tank to be converted to a clarifier tank, servicing of the pipe, need for increase in outflow capacity, etc. Replacement of such an underground pipe is difficult and very costly.
U.S. Pat. No. 5,340,485 showed a somewhat different system for collection of settled sludge from the floor of a clarifier. The patent shows a collection tube positioned radially outwardly from the center column, for drawing the sludge to an elevated position initially, then into the center column and down through an exit pipe. The withdrawal pipe in that system was located beneath the flow of the clarifier. A pump was positioned to withdraw the sludge. In one embodiment the sludge is drawn up almost to the liquid level in the tank, to a sludge collection box, into the center column and a vertical discharge pipe, then back down below the clarifier floor to an exit pipe. The patent also shows, in FIG. 5, a manifold device for use where the sludge enters the vertical discharge pipe, and a device similar to that manifold device can be used in the current invention, although in a different way.
It is an object of the invention to withdraw settled sludge from the floor of a clarifier into the center column of the clarifier and then upwardly and radially out from the clarifier without underground pipes, including retrofitting existing floor-effluent clarifiers to eject the settled sludge upwardly and outwardly. These and other objects, advantages and features of the invention will be apparent from the following description of a preferred embodiment, considered along with the accompanying drawings.